--- 1/draft-ietf-6tisch-6top-sf0-02.txt 2017-03-13 07:13:58.869100104 -0700 +++ 2/draft-ietf-6tisch-6top-sf0-03.txt 2017-03-13 07:13:58.897100766 -0700 @@ -1,23 +1,23 @@ 6TiSCH D. Dujovne, Ed. Internet-Draft Universidad Diego Portales Intended status: Standards Track LA. Grieco -Expires: May 4, 2017 Politecnico di Bari +Expires: September 14, 2017 Politecnico di Bari MR. Palattella Luxembourg Institute of Science and Technology (LIST) N. Accettura LAAS-CNRS - October 31, 2016 + March 13, 2017 6TiSCH 6top Scheduling Function Zero (SF0) - draft-ietf-6tisch-6top-sf0-02 + draft-ietf-6tisch-6top-sf0-03 Abstract This document defines a Scheduling Function called "Scheduling Function Zero" (SF0). SF0 dynamically adapts the number of allocated cells between neighbor nodes, based on the amount of currently allocated cells and the neighbor nodes' cell requirements. Neighbor nodes negotiate in a distributed neighbor-to-neighbor basis the number of cell(s) to be added/deleted. SF0 uses the 6P signaling messages to add/delete cells in the schedule. This function selects @@ -38,63 +38,65 @@ Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on May 4, 2017. + This Internet-Draft will expire on September 14, 2017. Copyright Notice - Copyright (c) 2016 IETF Trust and the persons identified as the + Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. TEMPORARY EDITORIAL NOTES . . . . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Scheduling Function Identifier . . . . . . . . . . . . . . . 4 4. SF0 Triggering Events . . . . . . . . . . . . . . . . . . . . 4 - 5. SF0 Cell Estimation Algorithm . . . . . . . . . . . . . . . . 5 + 5. SF0 Cell Estimation Algorithm . . . . . . . . . . . . . . . . 4 6. SF0 Allocation Policy . . . . . . . . . . . . . . . . . . . . 5 7. Rules for CellList . . . . . . . . . . . . . . . . . . . . . 6 8. 6P Timeout Value . . . . . . . . . . . . . . . . . . . . . . 7 9. Meaning of Metadata Information . . . . . . . . . . . . . . . 7 10. Node Behavior at Boot . . . . . . . . . . . . . . . . . . . . 7 - 11. Relocating Cells . . . . . . . . . . . . . . . . . . . . . . 7 - 12. Forced Cell Deletion Policy . . . . . . . . . . . . . . . . . 8 - 13. 6P Error Handling . . . . . . . . . . . . . . . . . . . . . . 8 - 14. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 8 - 15. Implementation Status . . . . . . . . . . . . . . . . . . . . 8 - 16. Security Considerations . . . . . . . . . . . . . . . . . . . 9 - 17. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 - 18. 6P Compliance . . . . . . . . . . . . . . . . . . . . . . . . 9 - 19. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10 - 20. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 - 20.1. Normative References . . . . . . . . . . . . . . . . . . 10 - 20.2. Informative References . . . . . . . . . . . . . . . . . 10 + 11. Cell Type . . . . . . . . . . . . . . . . . . . . . . . . . . 7 + 12. SF0 Statistics . . . . . . . . . . . . . . . . . . . . . . . 8 + 13. Relocating Cells . . . . . . . . . . . . . . . . . . . . . . 8 + 14. Forced Cell Deletion Policy . . . . . . . . . . . . . . . . . 8 + 15. 6P Error Handling . . . . . . . . . . . . . . . . . . . . . . 8 + 16. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 9 + 17. Implementation Status . . . . . . . . . . . . . . . . . . . . 9 + 18. Security Considerations . . . . . . . . . . . . . . . . . . . 9 + 19. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 + 20. 6P Compliance . . . . . . . . . . . . . . . . . . . . . . . . 10 + 21. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10 + 22. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 + 22.1. Normative References . . . . . . . . . . . . . . . . . . 10 + 22.2. Informative References . . . . . . . . . . . . . . . . . 11 Appendix A. [TEMPORARY] Changelog . . . . . . . . . . . . . . . 11 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 1. TEMPORARY EDITORIAL NOTES This document is an Internet Draft, so it is work-in-progress by nature. It contains the following work-in-progress elements: o "TODO" statements are elements which have not yet been written by the authors for some reason (lack of time, ongoing discussions with no clear consensus, etc). The statement does indicate that the text will be written at some time. @@ -114,36 +116,35 @@ This document defines a minimal Scheduling Function for the 6top sublayer [I-D.ietf-6tisch-6top-protocol], called "Scheduling Function Zero" (SF0). SF0 is designed to offer the minimal set of functionalities to be usable in a wide range of applications. SF0 defines two algorithms: The Scheduling Algorithm defines the number of cells to allocate/delete between two neighbours and the relocation algorithm defines when to relocate a cell. The Scheduling Algorithm: A number of TX and/or RX cells must be allocated between neighbor nodes in order to enable data transmission - among them. From the allocated cells, a part of them can be under - effective use by the neighbours, while the rest of cells are over- - provisioned to detect an increase in cell usage without packet loss. - The Scheduling Algorithm collects the cell allocation/deletion - requests from the neighbors and the number of cells which are - currently under usage. First, a Cell Estimation Algotithm calculates - the number of required cells by adding the collected values and - second, the calculated value is given to the Allocation Policy, which - provides stability by adding hystheresis and overprovisioning by - deciding when to schedule the new number of cells, according to a - threshold. In order to reduce consumption, this algorithm is - triggered only when there is a change on the number of effectively - used cells or if there is a change on the number of requested cells - from a particular node. + among them. A portion of these allocated cells will be utilized by + neighbors, while the remaining cells can be over-provisioned to + handle unanticipated increases in cell requirements. The Scheduling + Algorithm collects the cell allocation/deletion requests from the + neighbors and the number of cells which are currently under usage. + First, the Cell Estimation Algotithm calculates the number of + required cells by adding the collected values and second, the + calculated value is given to the Allocation Policy, which provides + stability by adding hystheresis and overprovisioning by deciding when + to schedule the new number of cells, according to a threshold. In + order to reduce consumption, this algorithm is triggered only when + there is a change on the number of effectively used cells or if there + is a change on the number of requested cells from a particular node. - The Relocation Algorithm: Allocated cells may experiment packet loss + The Relocation Algorithm: Allocated cells may experience packet loss from different sources, such as noise, interference or cell collision (after the same cell is allocated by other nodes in range on the network). In order to avoid this problem, Packet Delivery Rate (PDR) is monitored periodically for each allocated cell. A relocation is triggered when the PDR value drops below a certain threshold, compared to the average PDR of the rest of allocated cells. The destination location on the schedule is defined randomly. To synthesize, a node running SF0 determines when to add/delete cells in a three-step process: @@ -151,67 +152,64 @@ 1. It waits for a triggering event (Section 4). 2. It applies the Cell Estimation Algorithm (CEA) for a particular neighbor to determine how many cells are required to that neighbor (Section 5). 3. It applies the Allocation Policy to compare the number of required cells to the number of already scheduled cells, and determines the number of cells to add/delete (Section 6). We expect additional SFs, offering more functionalities for a more specific use case, to be defined in future documents. SF0 addresses - the requirements for a scheduling function listed in Section 5.2 - [TODO: update if needed] from [I-D.ietf-6tisch-6top-protocol], and - follows the recommended outline listed in Section 5.3 [TODO: update - if needed] of [I-D.ietf-6tisch-6top-protocol]. This document follows - the terminology defined in [I-D.ietf-6tisch-terminology]. + the requirements for a scheduling function listed in Section 5.2 from + [I-D.ietf-6tisch-6top-protocol], and follows the recommended outline + listed in Section 5.3 of [I-D.ietf-6tisch-6top-protocol]. This + document follows the terminology defined in + [I-D.ietf-6tisch-terminology]. 3. Scheduling Function Identifier The Scheduling Function Identifier (SFID) of SF0 is IANA_SFID_SF0. 4. SF0 Triggering Events We RECOMMEND SF0 to be triggered at least by the following events: - 1. If there is a change in the current number of used cells + 1. If there is a change in the current number of required cells 2. If there is a successful cell allocation/deallocation process with the neighbour. This allows SF0 to be triggered by any change in locally generated or incoming traffic. The exact mechanism of when SF0 is triggered is implementation-specific. 5. SF0 Cell Estimation Algorithm The Cell Estimation Algorithm takes into account the new incoming cell requirements from the neighbor node and the current outgoing - number of effectively used cells. This allows the algorithm to - estimate a new number of cells to be allocated. As a consequence, - the Cell Estimation Algorithm for SF0 follows the steps described - below: + number of used cells. This allows the algorithm to estimate a new + number of cells to be allocated. As a consequence, the Cell + Estimation Algorithm for SF0 follows the steps described below: - 1. Collect the new incoming cell requirements from the neighbor - 2. Collect the current number of effectively used cells - 3. Calculate the new number of cells to be allocated by adding the - current number of effectively used cells and the new incoming - cells requirement - 4. Submit the request to the allocation policy as REQUIREDCELLS - 5. Return to step 1 and wait for a triggering event. + 1. Collect the current number of used cells + 2. Calculate the new number of cells to be allocated by adding the + current number of used cells plus an OVERPROVISION number of + cells + 3. Submit the request to the allocation policy as REQUIREDCELLS + 4. Return to step 1 and wait for a triggering event. - A new incoming cell requirement is the result of a successful - allocation process from the neighbor. TODO/REMARK: Add a number of - cells to the required cells as OVERPROVISION to guarantee that the - growth on the effectively used cells can be identified without packet - loss. This value is implementation specific. A value of + The OVERPROVISION parameter is a percentage of the currently + allocated cells which is added to the used cells to guarantee that + the growth on the number of used cells can be detected without packet + loss. This percentage value is implementation-specific. A value of OVERPROVISION equal to zero leads to queue growth and possible packet loss, since there are no overprovisioned cells to detect if there is - a growth of effectively used cells. + a growth on the number of used cells. 6. SF0 Allocation Policy The "Allocation Policy" is the set of rules used by SF0 to decide when to add/delete cells to a particular neighbor to satisfy the cell requirements. SF0 uses the following parameters: SCHEDULEDCELLS: The number of cells scheduled from the current node @@ -219,21 +217,23 @@ REQUIREDCELLS: The number of cells calculated by the Cell Estimation Algorithm from the current node to that neighbor. SF0THRESH: Threshold parameter introducing cell over-provisioning in the allocation policy. It is a non-negative value expressed as number of cells. The definition of this value is implementation- specific. A setting of SF0THRESH>0 will cause the node to allocate at least SF0THRESH cells to each of its' neighbors. The SF0 allocation policy compares REQUIREDCELLS with SCHEDULEDCELLS and decides to add/delete cells taking into account SF0THRESH. This - is illustrated in Figure 1. + is illustrated in Figure 1. The number of cells to be scheduled/ + deleted is out of the scope of this document and it is + implementation-dependent. SCHEDULEDCELLS <---------------------------------> +---+---+---+---+---+---+---+---+---+ | | | | | | | | | | +---+---+---+---+---+---+---+---+---+ |<----------------->| | SF0THRESH | | | REQUIREDCELLS | | @@ -305,72 +305,88 @@ BIT 15 [WBLIST] is used to indicate that the CellList provided is a Whitelist (value=0) or a Blacklist (value=1). 10. Node Behavior at Boot In order to define a known state after the node is restarted, a CLEAR command is issued to each of the neighbor nodes to enable a new allocation process. The 6P Initial Timeout Value provided by SF0 should allow for the maximum number of TSCH link-layer retries, as defined by Section 4.3.4 of [I-D.ietf-6tisch-6top-protocol]. TODO/ - REMARK: The initial timeout is currently under discussion. + REMARK: The initial timeout is currently under discussion on the + Mailing List. -11. Relocating Cells +11. Cell Type + + SF0 uses TX (Transmission) cell type only, thus defining celloptions + as TX=0, RX=1 and S=0 according to section 4.2.6 of + [I-D.ietf-6tisch-6top-protocol]. + +12. SF0 Statistics + + Packet Delivery Rate (PDR) is calculated per cell, as the quotient of + the number of successfully delivered packets to 10, for the last 10 + packet transmission attempts, without counting retransmissions. + +13. Relocating Cells SF0 uses Packet Delivery Rate (PDR) statistics to monitor the currently allocated cells for cell relocation (by changing their slotOffset and/or channelOffset). When the PDR of one or more - softcells is below 20% of the average PDR of the rest of the - scheduled cells, SF0 relocates the cell(s) to a number of available - cells selected randomly. REMARK: This criteria is currently under - discussion; simulation/experimentation is required to either adjust - the threshold or to change the process. + softcells is below PDR_THRESHOLD, defined as a percentage of the + average of the PDR of the rest of the scheduled cells, SF0 relocates + each of the cell(s) to a number of available cells selected randomly. + PDR_THRESHOLD is out of the scope of this document and it is + implementation-dependent. -12. Forced Cell Deletion Policy +14. Forced Cell Deletion Policy - TODO: When all the cells are scheduled, we need a policy to free - cells, for example, under alarm conditions or if a node disappears - from the neighbor list. + When all the cells are scheduled, we need a policy to free cells, for + example, under alarm conditions or if a node disappears from the + neighbor list. The action to follow this condition is out of scope + of this document and it is implementation-dependent. -13. 6P Error Handling +15. 6P Error Handling A node implementing SF0 handles a 6P Response depending on the Return Code it contains: RC_SUCCESS: If the number of elements in the CellList is the number of cells specified in the NumCells field of the 6P ADD Request, the operation is complete. The node does not take further action. If the number of elements in the CellList is smaller (possibly 0) than the number of cells specified in the NumCells field of the 6P ADD Request, the neighbor has received the request, but less than - NumCells of the cells in the CellList were. In that case, the - node MAY retry immediately with a different CellList if the amount - of storage space permits, or build a new (random) CellList. + NumCells of the cells in the CellList were allocated. In that + case, the node MAY retry immediately with a different CellList if + the amount of storage space permits, or build a new (random) + CellList. RC_ERR_VER: The node MUST NOT retry immediately. The node MAY add the neighbor node to a blacklist. The node MAY retry to contact this neighbor later. RC_ERR_SFID: The node MUST NOT retry immediately. The node MAY add the neighbor node to a blacklist. The node MAY retry to contact this neighbor later. RC_ERR_GEN: The node MUST issue a CLEAR command tot he neighbour. RC_ERR_BUSY: Wait for a timeout and restart the scheduling process. + RC_ERR_NORES: Wait for a timeout and restart the scheduling process. RC_ERR_RESET: Abort 6P Transaction RC_ERR: Abort 6P Transaction. The node MAY retry to contact this neighbor later. -14. Examples +16. Examples TODO -15. Implementation Status +17. Implementation Status This section records the status of known implementations of the protocol defined by this specification at the time of posting of this Internet-Draft, and is based on a proposal described in [RFC6982]. The description of implementations in this section is intended to assist the IETF in its decision processes in progressing drafts to RFCs. Please note that the listing of any individual implementation here does not imply endorsement by the IETF. Furthermore, no effort has been spent to verify the information presented here that was supplied by IETF contributors. This is not intended as, and must not @@ -385,108 +401,116 @@ It is up to the individual working groups to use this information as they see fit". OpenWSN: This specification is implemented in the OpenWSN project [OpenWSN]. The authors of this document are collaborating with the OpenWSN community to gather feedback about the status and performance of the protocols described in this document. Results from that discussion will appear in this section in future revision of this specification. -16. Security Considerations +18. Security Considerations TODO -17. IANA Considerations +19. IANA Considerations o IANA_SFID_SF0 -18. 6P Compliance +20. 6P Compliance o MUST specify an identifier for that SF. OK o MUST specify the rule for a node to decide when to add/delete one or more cells to a neighbor. OK o MUST specify the rule for a Transaction source to select cells to add to the CellList field in the 6P ADD Request. OK o MUST specify the rule for a Transaction destination to select cells from CellList to add to its schedule. OK o MUST specify a value for the 6P Timeout, or a rule/equation to - calculate it. + calculate it. OK o MUST specify a meaning for the "Metadata" field in the 6P ADD Request. OK o MUST specify the behavior of a node when it boots. OK o MUST specify what to do after an error has occurred (either the node sent a 6P Response with an error code, or received one). OK o MUST specify the list of statistics to gather. An example statistic if the number of transmitted frames to each neighbor. In case the SF requires no statistics to be gathered, the specific - of the SF MUST explicitly state so. - + of the SF MUST explicitly state so. OK o SHOULD clearly state the application domain the SF is created for. OK o SHOULD contain examples which highlight normal and error scenarios. o SHOULD contain a list of current implementations, at least during the I-D state of the document, per [RFC6982]. o SHOULD contain a performance evaluation of the scheme, possibly through references to external documents. - o MAY redefine the format of the CellList? field. + o MAY redefine the format of the CellList? field. OK -19. Acknowledgments +21. Acknowledgments Thanks to Kris Pister for his contribution in designing the default Bandwidth Estimation Algorithm. Thanks to Qin Wang and Thomas Watteyne for their support in defining the interaction between SF0 and the 6top sublayer. This work is partially supported by the Fondecyt 1121475 Project, the Inria-Chile "Network Design" group, and the IoT6 European Project (STREP) of the 7th Framework Program (Grant 288445). -20. References +22. References -20.1. Normative References +22.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . -20.2. Informative References +22.2. Informative References [RFC6982] Sheffer, Y. and A. Farrel, "Improving Awareness of Running Code: The Implementation Status Section", RFC 6982, DOI 10.17487/RFC6982, July 2013, . [I-D.ietf-6tisch-terminology] Palattella, M., Thubert, P., Watteyne, T., and Q. Wang, "Terminology in IPv6 over the TSCH mode of IEEE - 802.15.4e", draft-ietf-6tisch-terminology-07 (work in - progress), March 2016. + 802.15.4e", draft-ietf-6tisch-terminology-08 (work in + progress), December 2016. [I-D.ietf-6tisch-6top-protocol] Wang, Q. and X. Vilajosana, "6top Protocol (6P)", draft- - ietf-6tisch-6top-protocol-02 (work in progress), July + ietf-6tisch-6top-protocol-03 (work in progress), October 2016. [OpenWSN] Watteyne, T., Vilajosana, X., Kerkez, B., Chraim, F., Weekly, K., Wang, Q., Glaser, S., and K. Pister, "OpenWSN: a Standards-Based Low-Power Wireless Development Environment", Transactions on Emerging Telecommunications Technologies , August 2012. Appendix A. [TEMPORARY] Changelog o draft-ietf-6tisch-6top-sf0-02 * Editorial changes (figs, typos, ...) + o draft-ietf-6tisch-6top-sf0-03 + + * Fixed typos + * Removed references to "effectively used cells" + * Changed Cell Estimation Algorithm to the third proposed + alternative on IETF97 + * Forced cell deletion becomes implementation specific + * Added PDR calculation formula + * Added PDR_THRESHOLD as implementation specific value Authors' Addresses Diego Dujovne (editor) Universidad Diego Portales Escuela de Informatica y Telecomunicaciones Av. Ejercito 441 Santiago, Region Metropolitana Chile